Prostate cancer is one of the most prevalent cancers in men. While most prostate cancers at early onset are symptom-free and slow growing, certain prostate cancers are more aggressive, painful and lead to fatality. At present, two major types of non-invasive screening tests are available for detection of prostate cancer in men. One is digital rectal exam (DRE), which allows a doctor to detect prostate abnormalities by inserting a gloved finger into the rectum and feeling the prostate gland, and the other is prostate surface antigen test (PSA test), which measures the level of the PSA antigen in a blood sample. Although FDA has approved use of PSA test together with DRE to help detect prostate cancer in men, the PSA test is controversial in screening as it is not clear whether the test actually saves lives. In particular, the United States Preventive Services Task Forces has recently recommended against PSA screening in healthy men, based on findings that PSA screening reduces no or little prostate cancer mortality while leading to treatments or tests that cause unnecessary pain and side effects (see, e.g., R. Chou et al, Ann. Intern. Med., Oct. 7, 2011 E-375; Djulbegovic et al, BMJ 2010, 341: c4543). The most definitive diagnosis of prostate cancer is biopsy, where a small piece of the prostate from the suspected patient is removed for microscopic examination for the presence of tumor cells. Obviously such procedure is rather invasive and less desirable in early screening and detection.
As in many other types of cancers, the main cause of death in prostate cancer patients is not the primary tumor but rather the metastasis. Some primary tumor cells can detach themselves from the original tissue and enter into circulation. These cells are called circulating tumor cells (CTCs). Once CTCs seed themselves to a suitable site in the body, they may develop into metastatic colonies that are difficult to detect yet can be life-threatening as they progress into secondary tumors. Attempts have been made to detect the CTCs. However, no methods have been developed that can distinguish if the CTCs are originated from prostate and how the prostate cancer has progressed. In view of the recent finding that PSA screening fails in reducing mortality, there remain significant needs for development of agents and methods that can provide reliable results in the diagnosis and prognosis of prostate cancer.